Anastomosis stent and stent selection system

ABSTRACT

A stent or support is disclosed for use in the connection or anastomosis of severed vessels to support and seal the anastomotic site. The stent includes substantially cylindrical sections separated by a tapered transitional region. The cylindrical sections are provided with flanges that define tapered sealing surfaces. The dimensions of the two sections are selected to correspond with the diameter of the portions of the vessel to be supported. The stent is preferably made of polyglycolic acid and the dimensions of the stent are selected to provide optimal support and sealing characteristics with a minimum of damage to the epithelial lining of the vas deferens. In three preferred applications, the stent is used in anastomosis of the severed ends of a vas deferens, a Fallopian tube, and a blood vessel. A gauge is used to measure the severed ends and, in that manner, determine the appropriate dimensions of the stent. A technique of forming porous stents, and other structures, is also disclosed.

This application is a continuation-in-part application based on priorcopending application Ser. No. 07/814,328, filed Dec. 23, 1991, now U.S.Pat. No. 5,192,289, which in turn is a continuation application based onprior application Ser. No. 07/689,669, filed on Apr. 23, 1991, and sinceabandoned, which, in turn, was a continuation application based on priorapplication Ser. No. 07/320,983, filed on Mar. 9, 1989 now abandoned andsince abandoned, the benefits of the filing dates of which are herebyclaimed under 35 U.S.C.§120.

FIELD OF THE INVENTION

This invention relates generally to stents and, more particularly, tostents for use in anastomosis.

BACKGROUND OF THE INVENTION

Fluid-carrying vessels exist in a wide number of systems, includingthose physiological systems found, for example, in the human body. Theassembly, modification, or repair of such systems frequently involvesthe connection or anastomosis of two or more vessels to define a fluidpath. To assist in anastomosis of physiological vessels, an internalsupport or stent may be employed at the vessel junction. The stentmaintains the desired orientation of the vessels and provides rigidityto the vessels at the point of connection, or anastomotic site. Inaddition, the stent may reduce leakage at the anastomotic site byconfining the fluid to a passage extending through the stent.

Given the nature of physiological vessels, their connection frequentlyrequires the use of a stent only until the vessel tissue reorganizes toprovide a continuous, healed conduit. One stent designed to provide suchtemporary support to physiological vessels is described in U.S. Pat. No.3,620,218. There, a cylindrical support made of polyglycolic acid isdisclosed for use in connecting a variety of vessels including bloodvessels, spermatic ducts, bile ducts, ureters and sinus tubes. Thisinternal support is located at the anastomotic site and supports thevessel ends, which are held together by sutures or clamps ofpolyglycolic acid. In one embodiment, the support has tapered ends tomake insertion into the vessel ends easier. In another embodiment, theends are slightly expanded to hold the vessels in place about thesupport. The reference also notes that the diameter of the support mayvary where vessels of different size are to be spliced.

While prior art supports have aided in the connection of physiologicalvessels, several problems may still be encountered. First, because aphysiological vessel is a relatively sensitive structure, it can beeasily damaged by a support arrangement that applies pressure to fixedportions of the vessel for extended periods. Further, when vessels ofvarying diameter are to be joined, the sharp transition in diameter atthe anastomotic site may lead to puckering of the vessel ends andmisalignment of the joined vessels. Finally, the ability of a particularsupport to be inserted into, and seal, a vessel may vary significantlywith even minor variations in vessel size. In light of theseobservations, it would be desirable to produce an anastomosis stent thatdoes not significantly injure the vessel, that allows a good connectionto be produced between vessels of different size, and that isdimensioned to produce optimal insertion and sealing characteristicswhen used with the particular vessels to be joined.

SUMMARY OF THE INVENTION

In accordance with this invention, a stent is provided for use in thereconnection of a severed vessel that may carry fluid and that has afirst free portion and a second free portion. The stent includes asupport for supporting the first and second portions of the vessel.Flanges are also provided on the support for sealably engaging the firstand second portions of the vessel. The flanges sealably engage the firstand second portions of the vessel in a manner that varies with use ofthe stent to minimize trauma to the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a pictorial view of the anastomotic site of a reconnected vasdeferens, supported by a stent constructed in accordance with thisinvention;

FIG. 2 is a pictorial view of the stent employed at the anastomotic siteof FIG. 1;

FIG. 3 is a longitudinally sectioned view of the stent of FIG. 2;

FIG. 4 is a pictorial view of a sizing gauge employed to measure theinner diameters of the testicular (proximal) and abdominal (distal)portions of the vas deferens;

FIG. 5 is a pictorial view of an alternative embodiment of the stent ofFIG. 2;

FIG. 6 is a pictorial view of an appliance for use in, for example,orthopedic reconstruction or drug delivery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an anastomotic site 10, supported by a hollowstent 12 constructed in accordance with this invention, is shown. Whilethe connection of fluid-carrying vessels in numerous physiologicalsystems can be supported in this manner, in the preferred embodiment,the stent 12 is constructed for use at the anastomotic site 10 producedby the surgical procedure known as a vasovasostomy. Before describingstent 12 in greater detail, a brief outline of this surgical procedureis provided.

Briefly, a vasovasostomy is the reversal of an earlier surgicalprocedure known as a vasectomy, which is used for male sterilization. Ina vasectomy, a small section of the vas deferens is surgically removedand the proximal and distal ends leading from the testicle and to theabdomen, respectively, are cauterized and tied. In a vasovasostomy thisprocess is reversed by surgically reconnecting the severed ends of thevas deferens. The testicular portion always swells an unknown, variableamount after being tied. Thus, a surgeon performing a vasovasotomy isfaced with the problem of joining vessels of differing diameters.

As will be appreciated, the success of this procedure depends on anumber of considerations. For example, if the tissue of the vas deferensis to reorganize normally, it must be maintained in close contact duringhealing. In addition, the anastomotic site must not be allowed tocollapse or the passage of sperm through the vas deferens will beblocked. To increase the likelihood of success, the stent 12 is insertedinto the severed ends of the vas deferens during the vasovasostomy tosupport the anastomotic site during tissue recombination. In thismanner, the desired alignment of the vas deferens is maintained duringhealing and the anastomotic site is prevented from collapsing.

Turning now to a detailed consideration of stent 12 and the advantagesof its construction, reference is made to FIGS. 2 and 3. As shown, stent12 can be roughly divided into three sections. A first section 14 isstructured to support and sealably engage the abdominal (distal) portionof the vas deferens. A second section 16 is constructed to sealablyengage and support the testicular (proximal) portion of the vasdeferens. A third section 18, located intermediate the first and secondsections 14 and 16, is designed to support the anastomotic site andprovide a smooth transition between the larger proximal and smallerdistal portions of the vas deferens.

Referring now to the first section 14, as shown in FIGS. 2 and 3, itincludes a cylindrical body portion 20 having a sealing flange 22 thatis spaced apart from the distal end 24 of stent 12 by a cylindrical endportion 26. The body portion 20 is hollow, having a coaxial cylindricalpassage 28 extending therethrough. As described in greater detail below,the body portion 20 has an outer diameter OD₁, an inner diameter ID₁, athickness t₁ , and a length L₁, particularly dimensioned for use withthe distal portion of the vas deferens.

Turning now to a discussion of flange 22, flange 22 generally resemblesthe frustum of a cone whose reduced-diameter end is oriented proximalthe end portion 26 of stent 12. As shown in FIG. 3, the flange 22 isundercut. Flange 22 includes an exposed sealing surface 30 that definesan obtuse angle θ₁ with the cylindrical end portion 26 of stent 12 andthat terminates in an outer rim 34. The inner surface of the flange 22is tapered at an angle θ₂, causing its thickness t₂ to decrease as therim 34 is approached. The flange 22 has a first outer diameter OD₂ atrim 34 and a second outer diameter OD₃ at the end of flange 22 adjacentend portion 26. Flange 22 has a length L₂.

The final portion of section 14 of stent 12 to be considered is thecylindrical end portion 26, located between the distal end 24 of stent12 and the flange 22. As shown in FIG. 3, end portion 26 has an outerdiameter OD₃ and an inner diameter ID₁ defined by cylindrical passage28. End portion 26 further has a wall thickness t₃ and a length L₃.

Addressing now the details of the second section 16 of stent 12, itsstructure corresponds to that of first section 14. More particularly,second section 16 includes a cylindrical body portion 36 having asealing flange 38 that is spaced apart from the testicular (proximal)end 40 of stent 12 by a cylindrical end portion 42. The body portion 36has an outer diameter OD₄ and an inner diameter ID₂, which is defined bya coaxial cylindrical passage 44. The body portion 36 also has a wallthickness t₄ and a length L₄.

Turning now to a description of flange 38, its general shape is that ofthe frustum of a cone whose reduced-diameter end is oriented proximalthe end portion 42 of stent 12. Flange 38 is undercut and includes anexposed sealing surface 46 that defines an obtuse angle θ₃ with thecylindrical end portion 42. The inner surface of flange 38 is tapered atan angle θ₄, causing the thickness t₅ of flange 38 to decrease as theouter rim 50 of flange 38 is approached. As shown in FIG. 3, the flange38 has an outer diameter OD₅ at rim 50 and an outer diameter OD₆adjacent end portion 42. Flange 38 has a length L₅.

The end portion 42 of the second section 16 of stent 12 extends betweenflange 38 and the testicular end 40 of stent 12. The end portion 42 hasan outer diameter OD₆ and an inner diameter ID₂ that is defined by acoaxial cylindrical passage 44. The wall thickness of end portion 42 isdesignated t₆, while its length is designated L₆.

Turning now to a discussion of the third section 18 of stent 12, asshown in FIGS. 2 and 3, section 18 joins the first and second sections14 and 16 of stent 12 and is shaped substantially like the frustum of acone. More particularly, it includes a tapered fluid passage 51 andtapered transitional support surface 52 that defines an obtuse angle θ₅with the surface of the cylindrical body portion 20 of first section 14.Given the axial alignment of the first and second sections 14 and 16,transitional surface 52 defines an angle θ₆ with the surface of thecylindrical body portion 36 of the second section 16 that is equal to360 degrees minus θ₅. The thickness of the third section is designatedt₇ and its length is designated L₇.

Having briefly reviewed the structure of stent 12, its role in theperformance of a vasovasostomy will now be considered. The first section14 and second section 16 are inserted into the severed ends of thedistal and proximal portions of the vas deferens. The sections areinserted a distance sufficient to place the severed ends of the vasdeferens in abutting contact, around the third section 18. The angularorientation of flanges 22 and 38 allows the first and second sections 14and 16 to be relatively easily inserted into the severed ends of the vasdeferens, but limits the ability of the severed ends to pull free ofstent 12 after insertion.

The confluent passages 28, 44, and 51 of stent 12 provide a conduit forthe flow of sperm through the reconnected vas deferens. Flanges 22 and38 provide a seal between the stent 12 and the connected portions of thevas deferens, preventing leakage at the anastomotic site. As shown inFIGS. 2 and 3, the second section 16 of stent 12 is proportionallylarger than the first section 14 to accommodate the larger diameter ofthe portion of the vas deferens coming from the testicle. Thisdimensional difference between the first and second sections 14 and 16,along with the orientation of flanges 22 and 38 prevents the stent 12from migrating out of the anastomotic site.

The third section 18 of stent 12 provides an anatomically correcttransition zone at the anastomotic site, allowing the larger testicularportion of the vas deferens to be secured to the smaller abdominalportion without pursing or puckering at the anastomotic site. As aresult, misalignment of the basement membrane and muscularis of the vasdeferens is avoided. In this regard, it is preferred that thetransitional surface 52 of section 18 be at an angle θ₅ of 170 degreeswith respect to body portion 20 and an angle θ₆ of 190 degrees withrespect to body portion 36.

The stent 12 is preferably made of a hydrolyzable medical plastic,allowing it to slowly break down by hydrolysis in the presence of spermfluid. The material becomes uniformly hydrated once it is immersed inaqueous fluid. The long-chain polymeric molecules become shorter andshorter, weakening the material uniformly. The residual strength of thematerial as it hydrolyzes is directly related to its thickness and bulk,thus, thinner sections will crumble more quickly than thick ones.Preferred materials include polyglycolic acid and polygalactin 9-10(e.g., manufactured by Ethicon, a division of Johnson & Johnson, underthe trademark VICRYL).

The process used to produce the stent is designed to take advantage ofthis tendency. Specifically, the stent 12 is molded initially to havedimensions slightly greater than those desired for the finished stent12. The stent 12 is then machined to shape the thinner flanges and tips,ensuring the desired sequential breakdown of the stent. Moreparticularly, machining induces stresses that enhance the rapid break-upof the flanges and tips of stent 12. The bulky tubular body, however,experiences minimal stress during machining and remains stronger for alonger time.

Given the tapered nature of the flanges 22 and 38, which are thinnest atrims 34 and 50, the flange seal diameters OD₂ and OD₅ are progressivelyreduced after implantation. This causes a corresponding reduction inseal pressure and a movement in the maximum seal pressure points definedby rims 34 and 50 as the rims 34 and 50 are broken down. The resultantshift in the maximum seal pressure points minimizes trauma to the liningepithelium of the vas deferens.

As breakdown continues, flanges 22 and 38 and end portions 26 and 42effectively disintegrate, allowing final tissue reorganization to occuraround the relatively tubular body portions 20 and 36 of the first andsecond sections 14 and 16. This progression is a result of the selectionof appropriate relative thicknesses for the various elements of stent12. More particularly, the thickness t₁ and t₄ of body portions 20 and36 is preferably twice the thickness t₃, t₆, t₂, and t₅ of end portions26 and 42 and flanges 22 and 38. Because the progress of stent 12breakdown is, in part, a function of thickness, end portions 26 and 42and flanges 22 and 38 will dissolve before the body portions 20 and 36and third section 18, thereby providing continued support and alignmentof the epithelial basement membranes at the anastomotic site where it ismost required during tissue reorganization. Ultimately, even theportions 18, 20, and 36 will dissolve, leaving the fully healed vasdeferens unobstructed.

While the construction and dimension of the various elements of stent 12described above can be varied, it has been found that a particularrelationship between the structure of stent 12 and the dimensions of theproximal and distal portions of the vas deferens, as determined by asizing gauge 54, described below, provides optimal performance. Moreparticularly, if the inner diameter of the distal (abdominal) portion ofthe vas deferens is designated S₁ and the inner diameter of the proximal(testicular) portion of the vas deferens is designated S₂, thedimensions of stent 12 will be as follows. OD₁ and OD₄ will be equal to70 percent of S₁ and S₂, respectively. Similarly, OD₂ and OD₅ will beequal to 100 percent of S₁ and S₂, respectively. Dimensions OD₃ and OD₆will be equal to 60 percent of S₁ and S₂, respectively. Dimensions ID₁and ID₂ will be equal to 50 percent of S₁ and S₂, respectively.

The thicknesses of the body portions 20 and 36 and third section 18 ofstent 12 are designated t₁, t₄, and t₇, as shown in FIG. 3. Preferably,t₁, t₄, and t₇ are equal to eight percent of S₂. The thicknesses of endportions 26 and 42 and the base of flanges 22 and 38, designated t₂, t₃,t₅ , and t₆, preferably are equal to one half that value or four percentof S2.

Turning now to the longitudinal dimensions of stent 12, the distancebetween flanges 22 and 38 of stent 12 is shown in FIG. 3 as the sum ofL₁, L₄, and L₇ and is preferably equal to 425 percent of S₁. With thisvalue fixed, it will be appreciated that the length of the third section18, designated L₇, is a function of the transitional surface angle θ₅and the difference between the outer diameters OD₁ and OD₄ of the firstand second sections 14 and 16. The remaining length between flanges 22and 38 is attributable equally to the dimensions L₁ and L₄.

Turning to the length L₂ of flange 22, it will be appreciated that it isfixed by the variation between OD₃ and OD₂, given the establishment ofθ₁ at a preferred angle of 155 degrees. Similarly, the length L₅ offlange 38 is geometrically determined by the variation between OD₅ andOD₆, given the preferred establishment of angle θ₃ at 155 degrees. Thelengths L₃ and L₆ of end portions 26 and 42, respectively, are less thanone-half of ID₁ and ID₂ to avoid occlusion by fragments of the tips onbreakdown.

A stent 12 constructed in accordance with the relationships set forthabove has been found to provide maximal flow of spermatic fluid throughstent passages 28, 44, and 51, minimal stent bulk and length, ease ofstent insertion into the vas deferens, adequate leakage protectionwithout the application of excess pressure to the epithelium of the vasdeferens, stent stability at the anastomotic site, anatomically correcttissue support surfaces at the anastomotic site, and relatively precisefitting of the stent to the vas deferens.

As will be appreciated, to provide a stent 12 that is dimensioned inaccordance with the relationships set forth above, it is necessary tofirst measure the inner diameters S₁ and S₂ of the proximal and distalportions of the vas deferens. To accomplish this, a double-ended gauge54 constructed as shown in FIG. 4 is employed.

More particularly, gauge 54 has a first end 56 that is used to measurethe inner diameter of the distal or proximal portions of the vasdeferens. A second end 58 is structured to allow the measurement of theinner diameter of the proximal (testicular) portion of the vas deferensin cases where the anastomotic site is close to the epididymus,preventing deep insertion to measure larger sizes. The ends 56 and 58are separated by a middle section 60 which allows gauge 54 to bemanipulated either manually or with the aid of surgical instruments.

As shown in FIG. 4, the first and second ends 56 and 58 of gauge 54comprise a plurality of axially aligned, cylindrical segments 62separated by tapered transitional sections 64. The diameters of thevarious segments 62 have a predetermined relationship with respect toeach other. On each end 56 and 58, the segment 62 having the largestdiameter is positioned adjacent the middle section 60 of gauge 54. Thediameters of the remaining segments 62 become progressively smaller withdistance from middle section 60.

As shown in FIG. 4, in the preferred arrangement, the first end 56 ofgauge 54 includes eight segments 62 identified by reference letters Athrough H. The outermost segment 62 is designated A and has a diameterthat is 0.005 inches (0.013 centimeters) less than the smallest expectedinner diameter for the distal portion of the vas deferens. Preferably,the diameter of segment A is equal to 0.025 inches (0.06 centimeters)and each subsequent segment increases in diameter by an increment of0.005 inches (0.013 centimeters), resulting in a diameter at segment Hof 0.060 inches (0.15 centimeters). The transition between adjacentsegments 62 is preferably uniform, with each transitional section 64defining an angle θ₇ of 155 degrees with respect to the preceding distalsegment 62.

At the second end 58 of gauge 54, seven additional sections, designatedI through O, are provided as shown in FIG. 4. The distal segment 62,designated I, has a diameter selected to correspond to the smallestexpected inner diameter of the proximal (testicular) portion of the vasdeferens. The diameter of the cylindrical segment 62, designated O,adjacent middle section 60 is 0.005 inches (0.013 centimeters) greaterthan the largest expected inner diameter of the proximal portion of thevas deferens. A uniform increment in the cylindrical segments betweenadjacent segments 62 is provided by the transitional sections 64, whichdefine a 155-degree angle with respect to the preceding distal segment62. The outer diameter of segment I is preferably 0.045 inches (0.11centimeters) with a 0.005 inch (0.013 centimeter) incremental transitionbetween adjacent segments resulting in a diameter at segment O of 0.075inch (0.19 centimeters). In the preferred arrangement, the dimensions ofsegments E, F, G, and H on end 56 correspond to those of segments I, J,K, and L, respectively, on second end 58.

The gauge 54 is used to determine the sizes S₁ and S₂ of the abdominaland testicular portions of the vas deferens in the following manner. Theappropriate end of the gauge 54 is inserted into the portion of the vasdeferens to be measured, after that portion has been prepared foranastomosis. Gauge 54 is inserted until it begins to dilate the vasdeferens and the vas deferens tightens around the segment 62 of gauge 54whose diameter corresponds to the inner diameter of the vas deferens.Ultimately, the wall of the vas deferens halts the advance of the gauge54. Because the diameters of the various segments 62 of gauge 54 areknown, the inner diameter of the vas deferens can then easily bedetermined. As will be appreciated, the accuracy of this determinationis a function of both the number of gauge segments 62 employed and thevariation in diameter between adjacent segments 62. This process isrepeated for both portions of the vas deferens. If a selection of stents12 is provided having dimensions conforming to the various combinationsof measured vas deferens sizes S₁ and S₂, these measurements can then beused to select an appropriately dimensioned stent 12 for use in thevasovasostomy.

With the appropriate stent 12 selected, the first and second sections 14and 16 of the stent 12 are then inserted into the severed ends of thedistal and proximal portions of the vas deferens. As a result, thesevered ends of the vas deferens are placed in abutting contact adjacentthe third section 18 of stent 12, in the manner described above. At thistime, a surgeon reconnects the severed ends, e.g., with sutures 66,staples 68, or heat from a laser. As shown, the sutures 66 or staples 68are spaced around the circumference of the anastomotic site and onlypartially penetrate the wall of the vas deferens, failing to reach thestent 12. In a preferred embodiment, sutures 66 or staples 68 are madeof the same hydrolyzable medical plastic, e.g., polyglycolic acid, asstent 12, and are absorbed, leaving no residual foreign material at theanastomotic site.

The preceding discussion is focused primarily on the use of stent 12 inthe performance of the surgical procedure of vasovasostomy. As will beappreciated, however, stents 12 constructed in accordance with thisinvention can be used in anastomosis of other fluid-carrying vessels.For example, other physiological applications for stent 12 include theperformance of Fallopian tube anastomosis and blood vessel anastomosis.

Blood vessel anastomosis obviously involves the surgical reconnection ofthe severed ends of a blood vessel. The vessel may have been necessarilysevered as part of a primary surgical operation performed on the patientor may be the result of some extrasurgical trauma suffered by thepatient. Unlike the severed ends of the vas deferens, the ends of theblood vessel will generally be of roughly the same diameter.

As with vasovasostomy, the successful anastomosis of a blood vesseldepends on a number of considerations. The inner diameter of theanastomotic site must be kept relatively large to prevent excessive flowresistance at the site. Low flow resistance is particularly important inblood vessel anastomosis to ensure adequate perfusion of downstreamtissue and to avoid elevating the blood pressure at the anastomotic siteto a point that inhibits vessel reorganization.

Successful blood vessel anastomosis also requires the provision of anenvironment in which the inner lining of the blood vessel, formed by alayer of endothelial cells, is free to migrate across the damaged areaof the vessel and proliferate over a basement layer of smooth musclecells and microvascular tissue. In addition, the anastomotic processshould not traumatize the endothelium around the anastomotic site orvessel reorganization will be inhibited.

In view of the constraints of blood vessel anastomosis, certain changesmay be advantageously made to a stent 12 constructed for use in thisapplication. For example, to ensure low flow resistance at theanastomotic site, the stent 12 has a relatively large inner diameter.One factor contributing to the ability to employ a stent having a largeinner diameter is the use of the stent to dilate the vessel to, forexample, roughly twice its normal diameter. Also, by relying upon thehighly stretched blood vessel wall to increase the forces applied to theflanges, narrower flanges can be employed, allowing a larger innerdiameter to be achieved for a given maximum stent diameter.

To assist the migration of endothelial cells across the inner lumen of atubular stent used, for example, in the anastomosis of a blood vessel, acontinuous network of spaces should be present throughout the body ofthe stent. As a result, blood is able to soak through the stent andsubsequently form a clot within it. The endothelium can then migrateacross the inner surface of the stent and attach to the clot, whichprotrudes from the pores on the stent's inner surface. Smooth musclecells and microvascular tissue eventually penetrate and replace the clotfrom the outer surface. As the stent dissolves, the resulting solutionwill be absorbed by the tissue growing in to fill the space onceoccupied by the stent.

A porous stent 70, of the type described above, is shown in FIG. 5.Stent 70 can be made by fusing preformed microspheres 72 of polyglycolicacid into the desired shape, leaving an array of pores 74 distributedthroughout the stent. The microspheres 72 used to form a blood vesselstent have a diameter of roughly 0.020-0.05 cm, although larger orsmaller microspheres may be employed depending upon the size and desiredstrength of the structure being formed, as well as the desired level ofporosity. The size of pores 74 is a function not only of the size of themicrospheres, but of the particular controls (e.g., pressure,temperature, duration) placed upon the fusion of the microspheres aswell. In the preferred arrangement, pore diameters range between0.005-0.015 cm.

In one technique used to fuse the microspheres together, the spheres areplaced in a split mold under pressure. The split mold is provided with acenter mandrel to form the interior of the tube. The mold is heated to235 degrees C (i.e., 455 degrees F) for a few seconds to sinter themicrospheres, melting their surfaces and fusing them together. The moldis then quickly cooled to ensure solid fusing of the microsphereswithout substantial degradation of the pores formed betweenmicrospheres. After the mold has cooled, the mandrel is withdrawn fromthe stent and the halves of the mold are opened, allowing the porousstent to be removed from the mold.

Another alternative technique employed to fuse the microspheres togetherinvolves the use of a solvent. The microspheres are again placed in asplit mold having a center mandrel. An inlet tube allows the solvent tobe introduced into the mold and passed over the spheres before leavingthe mold via an outlet tube. One suitable solvent ishexafluoroisopropynol. The solvent is passed over the microspheres for afew seconds, fusing the spheres together. The mold and fused stent arethen immediately flushed with a fixing or rinsing agent, such as water,to halt further fusing of the microspheres.

In contrast to the vasovasostomy stent, because the severed ends of theblood vessel are roughly the same diameter, the blood vessel stent 12 istypically symmetrically dimensioned about section 18. The blood vesselstent also is preferably shorter than the vasovasostomy stent to reducethe region of the endothelial layer that is potentially exposed totrauma during placement of the stent.

Although the construction and dimensions of the various elements of ablood vessel stent 12 can be varied, it has been found that a particularrelationship between the structure of the stent 12 and the dimensions ofeither end of the severed blood vessel, as determined by the sizinggauge 54, provides optimal performance. More particularly, if the innerdiameter of the blood vessel measured at either end is designated S₃ thedimensions of the stent 12 will be as follows. OD₁ and OD₄ will be equalto 75 percent of S₃. Similarly, OD₂ and OD₅ will be equal to 100 percentof S₃. Dimensions OD₃ and OD₆ will be equal to 70 percent of S₃.Dimensions ID₁ and ID₂ will be equal to 58 percent of S₃.

The length of the stent 12, equal to L₁ +L₂ +L₃ +L₄ +L₅ +L₆ +L₇, ispreferably 500 percent of S₃. Dimensions t₁, t₄, and t₇ are equal tosome first percentage of S₃, while dimensions t₂, t₃, t₅, and t₆ arepreferably equal to some second percentage of S₃. The angles θ₁ and θ₃are each equal to 155 degrees and the angles θ₅ and θ₆ are each equal to180 degrees.

Although the preceding discussion emphasizes the construction and oftubular stents and their use in, for example, the anastomosis of bloodvessels and vas deferens, the disclosed techniques and structures havebroader applicability. In that regard, microshperes can be fusedtogether in the manner described above to form porous structures havinga variety of applications. For example, urological and gastrointestinalstents can be manufactured in this manner. The fusion of microspherescan also be used to form an absorbable appliance 76, shown in FIG. 6,for other applications. In that regard, the appliance 76 may be designedfor orthopedic reconstruction, with the porous spaces 78 between themicrospheres 80 being filled with material 82, such as tissue (e.g.,bone). As another alternative, the material 82 permeating the porousspaces 78 may be a drug, with appliance 76 use as a drug delivery deviceto effect the timed release of the drug as the appliance dissolves inthe patient's system.

Those skilled in the art will recognize that the embodiments of theinvention disclosed herein are exemplary in nature and that variouschanges can be made therein without departing from the scope and thespirit of the invention. In this regard, and as was previouslymentioned, the invention is readily embodied in various applicationswith various means of connection employed to the vessels. Further, itwill be recognized that the dimensions and constructions of the stentcan be varied in conformity with the objective set forth. In addition,alternative approaches to the construction of stents may be used,including, for example, the machining or molding of the stent, as wellas any structural components or pores included with the stent. Becauseof the above and numerous other variations and modifications that willoccur to those skilled in the art, the following claims should not belimited to the embodiments illustrated and discussed herein.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A stent for use in thereconnection of first and second portions of a severed vessel that maycarry fluid, said stent comprising:a tube for supporting the first andsecond portions of the vessel, said tube having first and secondsections that are insertable into the first and second portions of thevessel, said first and second sections having first and second outersurfaces and terminating in first and second ends, respectively, saidtube including an inner passage extending between said first and secondends, the outer diameter of said first section of said tube being afirst predetermined function of the inner diameter of the first portionof the vessel, the outer diameter of said first end of said firstsection of said tube being a second predetermined function of the innerdiameter of the first portion of the vessel, the outer diameter of saidsecond section of said tube being a third predetermined function of theinner diameter of the second portion of the vessel, the outer diameterof said second end of said second section of said tube being a fourthpredetermined function of the inner diameter of the second portion ofthe vessel; and first and second flanges provided on said first andsecond outer surfaces of said tube, respectively, to sealably engage thefirst and second portions of the vessel, said first flange including afirst seal surface that defines an obtuse angle with respect to saidfirst outer surface extending toward said first end, said second flangeincluding a second seal surface that defines an obtuse angle withrespect to said second outer surface extending toward said second end,the outer diameter of said first flange being a fifth predeterminedfunction of the inner diameter of the first portion of the vessel, theouter diameter of said second flange being a sixth predeterminedfunction of the inner diameter of the second portion of the vessel, saidtube in said first and second flanges being made of a material thatdissolves when exposed to fluid.
 2. The stent of claim 1, wherein thefirst and third predetermined functions are 75 percent, the second andfourth predetermined functions are 70 percent, and the fifth and sixthpredetermined functions are 100 percent.
 3. The stent of claim 1,wherein the length of the stent is a seventh predetermined function ofthe inner diameter.
 4. The stent of claim 3, wherein the seventhpredetermined function is 500 percent.
 5. The stent of claim 1, whereinthe vessel said stent is for use with is a blood vessel.
 6. A stent foruse in the reconnection of a severed vessel that may carry fluid andthat has a first free portion and a second free portion, said stentcomprising:support means for supporting the first and second portions ofthe vessel, said support means having first and second sections that areinsertable into the first and second free portions of the vessel, saidfirst and second sections having first and second outer surfaces andterminating in first and second ends, respectively; and first and secondflanges provided on said first and second outer surfaces of said supportmeans, respectively, to sealably engage the first and second portions ofthe vessel, said first flange including a first seal surface thatdefines an obtuse angle with respect to said first outer surfaceextending toward said first end, said second flange including a secondseal surface that defines an obtuse angle with respect to said secondouter surface extending toward said second end, said support means andsaid first and second flanges being made of a material that dissolveswhen exposed to fluid, allowing the seal between the first seal surfaceand the first portion of the vessel and the seal between the second sealsurface and the second portion of the vessel to vary during use of saidstent to minimize trauma to the vessel.
 7. The stent of claim 6, whereinsaid support means comprises a tube having an inner passage extendingbetween said first and second ends.
 8. A stent for use in thereconnection of first and second portions of a severed vessel that maycarry fluid, said stent comprising:a porous tube formed of micospheresand having proximal and distal ends for supporting the first and secondportions of the vessel, said tube having first and second sections thatare insertable into the first and second portions of the vessel; andfirst and second porous flanges provided on said first and secondsections of said porous tube, respectively, to sealably engage the firstand second portions of the vessel, said tube and said first and secondflanges spaced from said proximal and distal ends being made of amaterial that dissolves when exposed to fluid.